Gradient barrier in a secondary recovery operation to inhibit water coning

ABSTRACT

The advance of the interface between subterranean hydrocarbon bearing formation fluids containing hydrocarbons and an underlying aquifer in a secondary recovery operation as it advances toward production perforations in a well bore to result in water coning during production is delayed by the imposition of reciculating barrier of an extraneous fluid, such as produced fluid hydrocarbons, injected into the subterranean hydrocarbon bearing formation via well perforations intermediate injection (lower) and production (upper) perforations in the well bore, the recirculation of the produced fluid hydrocarbons providing a gradient barrier.

[ GRADIENT BARRIER IN A SECONDARY RECOVERY OPERATION TO INHIBIT Y United States Patent [.161

Hoyt

WATER CONING [75] Inventor: Donald L. Hoyt, Houston, Tex.

[73] Assignees Texaco Inc., New York, N.Y.

. 22 Filed: Dec. 22, 1972 A [21] Appl. No.: 317,845

52 Us. Cl. 166/306 [51] Int. Cl E21b 43/20 [58] Field of Search 166/306, 305 R, 269, 245

[56] References Cited UNITED STATES PATENTS I,

2,607,426 8/1952 Rose 166/306 2,832,416 4/1958 Allen 166/306 X 2,886,108 5/1959 Piety.....- 166/306 3,195,633 7/1965 Jacob 166/306 3,199,592 8/1965 Jacob 166/306 3,386,514 6/1968 Weber 166/306 3,467,191 9/1969 Van Daalen et a1 166/269 MEX j July 23, 1974 3,593,787 Hoyt 166/245 Primary Examiner-Stephen J. Novosad Attorney, Agent, or Firm-Thomas H. Whaley; C. G.

Ries

, [57] ABSTRACT The advance of the interface between subterranean hydrocarbon bearing formation fluids containing hydrocarbons and an underlying aquifer in a secondary recovery operation as it advances toward production.

9 Claims, 2 Drawing Figures 2/1970 Weber et a1. 166/306 1 GRADIENT BARRIER IN A SECONDARY RECOVERY OPERATION TO INHIBIT WATER CONING FIELD OF THE INVENTION This invention relates generally to the production of hydrocarbons from a subterranean hydrocarbon bearing formation, and more particularly, to a method for overcoming water coning, which may result during the exploitation of a hydrocarbon bearing formation which overlays a water bearing formation, i.e. an aquifer.

DESCRIPTION. OF THE INVENTION I Water coning is a term given to the phenomenon of the entry of bottom waters into a production well. Under static conditions, water, having a greater density than formation hydrocarbon fluids, remains at the bottom of the production well. At high rates of production,

, however, the interface between the formation fluids including hydrocarbons and the underlying aquifer rises toward the production perforations due to the pressure gradients, and may extend into the well bore, because the upwardly directed pressure gradients associated with the flow of formation fluids intothe production perforations are able to balance the hydrostatic head of the resulting elevated water column.

Various methods have been proposed to eliminate o to reduce the water coning phenomenon. These methods have included reducing the depth of the well penetration into the hydrocarbon bearing formation, so that higher production rates are possible, without, at the same time, experiencing an excessive production of water therewith. g

In the commonly assigned US. Pat. No. 3,593,787, a gradient barrier is used in a horizontal sense, without the application of gravity, for controlling the advance of the interface in a secondary recovery program, by changing the function of I control wells at strategic times.

SUMMARY OF THE INVENTION cient upward vertical displacement, with reinjection of part of the produced formation fluids intermediate such perforations, all at controlled rates, will provide a gradient barrier in the form of a stable cycling envelope to suppress bottom water coning.

Other objects, advantages and features of this invention will become apparent from a consideration of the specification with reference to the figures of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS F l0. 1 schematically illustrates the water coning phenomenon; and

FIG. 2 schematically illustrates a method in accordance with this invention for overcoming water conin g.

Referring now to FIG. 1 0f the drawing which sche matically illustrates the water coning phenomenon, a subterranean hydrocarbon bearing formation is indicated at 11', and an immediately underlying, water heating formation is indicated at 12. A well bore 13 extends through the hydrocarbon bearing formation 11 and into the water bearing formation 12. A production casing 14 is provided with perforations 15 within the hydrocarbon bearing formation 11. Under static conditions, or at a relatively low rate of hydrocarbon production from the formation 11, the upper surface of the water bearing formation, i.e., the interface therebetween, is located at about the position indicated by the dashed line 16. At relatively high rates of production,

however, because of the upwardly directed pressure gradients associated with the flow of formation hydrocarbon fluids intoperforations 15, the watertable rises Referring now to FIG. 2 of the drawing, there is schematically illustrated therein a method according to this invention for preventing and/or reducing water coning. Thesame reference numerals have been employed in FIG. 2 as were employed in FIG. 1 for the same or similar elements, for reasons of clarity and ease of understanding. Asindicated in FIG. 2, well bore 13 is provided with an outer casing 14 and extends through hydrocarbon bearing formation 11, and into underlying water bearing formation 12.

In order to apply the method of this invention to prevent and/or reduce water coning when the secondary recovery operation production of formation hydrocarbon fluids is commenced via upper perforations 15 of outer casing 14 within the hydrocarbon bearing formation 11, packer 18 is inserted between outer casing 14 and inner conduit 19, above the lower perforations 20 in casing 14. Eventually, the interface of the fluids in formations 11 and 12 will be located below this packer, as indicated by dashed line 16. After the packer 18 has been installed, injection of water to create a bottom water drive is possible via inner conduit 19 into theformation 12 through lower perforations 20 in casing 14.

However, to inhibit water coning, an intermediate conduit 21, located in the annulus between casing 14 A-is maintained. This results when the water, injected in the zone C, has to travel a longer flow path around the envelope, as indicated by the depressed interface 16, FIG. 2. Thus, when a unit volume of water .reaches point P, its distance from the upper production perforations is suchthat the gravitational force acting downwardly is greater than the upward components due to injection and production gradients. The balance point depends on injection and production rates, densities of fluids, and geometry. Fluid flow from zone B should have flow rates adjusted to prevent a direct flow to zone A. q v

When required, the intermediate perforations 23, may be moved up the weli bore, afterthe water level has risen, to maintain blockage of water from the upper production perforations. Usually, the intermediate perforations are approximately halfwaybetween injection and production perforations, and the fluids injected via theintermediate perforations 23 in zone C are in the range of about to about 50% of the produced formation fluids'via the upper perforations in zone A.

The choice of barrier fluid isa matter of economics and availability. Recovered formation hydrocarbonfluids from produced formation fluids are a readily available supply sourceand can be' recovered with little extra expense. Other extraneous fluids may include such recovered productionlfluids treated with thickeners, butane and propane, all being misciblewith formation fluids, for ease in ultimate recovery of the gradient barrier. j

Thus, there has been shown and described the manner in which water coning is inhibited after the creation of a bottom water drive, by injecting an extraneous fluid into a hydrocarbon bearing formation via perforations intermediate the lower injection perforations and the upper production perforations to create a gradient barrier.

As will be apparent-to those skilled in the art in the light of the accompanying disclosure, other changes and alterations are possible in the practice of this invention without departing from the spirit or scope thereof.

lclaim:

1. A method of producing formation fluids including hydrocarbons from a subterranean hydrocarbon bearing formation under the' influence of an aquifer which comprises penetrating a well bore through said formation and into said aquifer, providing upper and lower perforations in said well bore respectively for communication with said formation and with said aquifer, producing said formation fluids including hydrocarbons 4 from said formation while injecting water into said aquifer to create a bottom water drive, providing perforations in said well bore intermediate said upper and lower perforations and thereafter injecting an extraneous fluid into said formation to provide a gradient barrier adjacent said well bore between said hydrocarbon bearing formation and said aquifer while maintaining formation fluid hydrocarbons from produced forma.

tion fluids, and then injecting a portion of the recoveredjfluid hydrocarbons into said formation via said intermediate perforations. i

4. In the method as defined in claim 3, said portion being inthe' range of about 10 percent to about percent of the recovered fluid hydrocarbons.

5. In the method as defined in' claim 3, said portion of recovered fluid hydrocarbons injected via'said intermediate perforations being treated with thickeners.

6. A method of inhibiting water coning wherein fluid hydrocarbons are produced from'a hydrocarbon bearing formation overlying a'water bearing formation and being penetrated by a well bore extending into said last mentioned formation which comprises introducing sufficient water into saidlast mentioned formation to create a bottom water drive and producing formation hy- I drocarbon fluids from said hydrocarbon bearing formation while injecting an extraneous fluid into the formation below the level at which said formation fluids are produced from the formation and above the level at which water is being introduced into the formation so that the extraneous fluid forms a stable cycling envelope.

7. In the method as defined in claim 6, said extraneous fluid being selected from the group consisting of butane,propane and produced hydrocarbon fluids.

8. In the method as defined in claim 7, the amount of said extraneous fluid comprising produced hydrocarbon fluids in the range of about 10 percent to about 50 percent of the total of produced formation fluids.

9. A method as defined in claim 6 wherein said water and said extraneous fluid are introduced into said formation'via the same well as is used for production of hydrocarbons from the formation. 

2. In the method as defined in claim 1, said extraneous fluid injected via the intermediate perforations being selected from the group consisting of butane, propane and produced hydrocarbon fluids.
 3. In the method as defined in claim 1, recovering formation fluid hydrocarbons from produced formation fluids, and then injecting a portion of the recovered fluid hydrocarbons into said formation via said intermediate perforations.
 4. In the method as defined in claim 3, said portion being in the range of about 10 percent to about 50 percent of the recovered fluid hydrocarbons.
 5. In the method as defined in claim 3, said portion of recovered fluid hydrocarbons injected via said intermediate perforations being treated with thickeners.
 6. A method of inhibiting water coning wherein fluid hydrocarbons are produced from a hydrocarbon bearing formation overlying a water bearing formation and being penetrated by a well bore extending into said last mentioned formation which comprises introducing sufficient water into said last mentioned formation to create a bottom water drive and producing formation hydrocarbon fluids from said hydrocarbon bearing formation while injecting an extraneous fluid into the formation below the level at which said formation fluids are produced from the formation and above the level at which water is being introduced into the formation so that the extraNeous fluid forms a stable cycling envelope.
 7. In the method as defined in claim 6, said extraneous fluid being selected from the group consisting of butane, propane and produced hydrocarbon fluids.
 8. In the method as defined in claim 7, the amount of said extraneous fluid comprising produced hydrocarbon fluids in the range of about 10 percent to about 50 percent of the total of produced formation fluids.
 9. A method as defined in claim 6 wherein said water and said extraneous fluid are introduced into said formation via the same well as is used for production of hydrocarbons from the formation. 